1. Field of the Invention
The present invention relates to a method of recording information in a phase-change optical recording medium, reproducing information therefrom, and rewriting information recorded in the phase-change optical recording medium.
The present invention also relates to an apparatus which is capable of recording information in a phase-change optical recording medium, reproducing information therefrom, and rewriting information recorded in the phase-change optical recording medium by use of the above-mentioned method.
2. Discussion of Background
For improving the quality of recording signals in the phase-change recording, various recording compensation methods have been disclosed.
For example, Japanese Laid-Open Patent Application 63-266632 discloses, as an effective method for improving the quality of recording signals, a method of recording long amorphous marks by use of a pulse string in a PWM (pulse width modulation) recording, using a recording film having a high crystallization speed.
In Japanese Laid-Open Patent Application 63-266633 and U.S. Pat. No. 5,150,351, a laser energy level of a pulse string is increased at a leading edge and a trailing edge of the pulse string, or the duration of irradiation is lengthened, whereby the jitters of the mark edge positions are controlled and the quality of recording signals is improved.
Furthermore, as disclosed in Japanese Patent Publication 63-29336, there is known a method of recording information signals in an optical disk by use of an optical disk recording apparatus by having a light spot of a laser beam scan the optical disk as the optical disk is irradiated with the laser beam, and by subjecting the light spot of the laser beam to power modulation.
There is also known a method for appropriately adjusting and setting the recording conditions such as light power for recording and the width of recording light pulse by reproducing information signals recorded in the optical disk, and monitoring the amplitude of the reproduced signals and the length of recording marks.
Furthermore, Japanese Laid-Open Patent Applications 9-138946, 9-138947, and 9-219021 disclose, as a method of improving the quality of recording signals, a method of recording and reproducing information in an information recording medium as shown in FIG. 1, wherein when information is recorded in the information recording medium by modulating an input signal and conducting pulse width modulation recording,
(A) a recording pulse string for recording and rewriting, corresponding to a zero (0) signal with a signal width nT, in which n is a positive integer, and T is a clock unit time, after the modulation of the input signal, is a continuous electromagnetic wave with a power level e, and
(B) a recording pulse string for recording and rewriting, corresponding to a one (1) signal with a signal width nT, in which n is a positive integer, and T is a clock unit time, after the modulation of the input signal, is an electromagnetic wave pulse string having:
a front-pulse portion fp with a power level a and a pulse duration period x,
a multi-pulse portion mp comprising a low-level pulse with a power level b and a high-level pulse with a power level c, with a total pulse duration period T and a duty ratio y, alternately repeating (n-n′) times continuously, and
an off-pulse portion op with a power level d and a pulse duration period z, in which x, y and z respectively satisfy 0.5T≦x≦2.0T, 0.125≦y≦0.875, and 0.125T ≦z≦1.0T, n′ is a positive integer which satisfies the condition of n′≦n, and (a and c) ≧e≧(b and d).
These prior art references also disclose an apparatus for recording and reproducing information in an information recording medium by use of the above-mentioned method.
The above-mentioned method, however, is not always suitable for improving the quality of recording signals in phase change recording when multi-speed recording or CAV (constant angular velocity) recording is carried out.
Recently, in a rewritable information recording medium, in particular, in the phase-change optical recording medium, there is a keen demand for a technology that makes it possible to record information at a plurality of different linear velocities in one information recording medium. Furthermore, high speed recording is in demand. As a matter of course, the CAV recording which is advantageous to the attainment of high speed recording is also in demand.
However, the technologies described in the above-mentioned prior art references, Japanese Laid-Open Patent Applications 9-138946, 9-138947, and 9-219021, cannot meet the above-mentioned demands. Specifically, for example, a recording strategy having fp, mp and op, which is capable of recording at a 4× CD linear speed, cannot obtain sufficiently high signal quality at an 8× speed recording and at a 10× speed recording when multiple recording is conducted at the 8× speed recording and the 10× speed recording.